Quickly and accurately estimating locations of things (e.g., a receiver) in a geographic area can be used to speed up emergency response times, track business assets, and link consumers to nearby businesses. Various techniques are used to estimate the position of the receiver, including a technique called trilateration, which is the process of using geometry to estimate the position of a receiver using distances traveled by different signals that are transmitted from geographically-distributed transmitters and later received by the receiver.
In many cases, the signals transmitted by geographically-distributed transmitters are received by the receiver at or near the same time, which makes it necessary for the receiver to distinguish each signal from other signals in order to determine the travel time of that signal for use during trilateration processing. Each transmitter may code its signal so the receiver can effectively identify that signal from other signals. As described later herein, however, designing and operating systems and methods for selecting different codes at various transmitters requires careful consideration of various issues.